Jake Gyllenhaal

Role: Lou Bloom, NightcrawlerTechnique: Gyllenhaal ran to get in the mindset of Nightcrawler's sociopathic journalist. And he ran a lot—15 miles each day to the film's set. He ended up losing almost 30 pounds and experiencing almost-hallucinations during his runs that involved feelings of being one with L.A.'s coyotes. Worth it? TBD. Critics are raving over Gyllenhaal's creepy performance, even throwing Gyllenhaal's name in the mix for awards season. —Ariana Bacle

Marlon Brando

Roles: All of themTechnique: Brando made Constantin Stanislavski's Method-ology famous (and infamous) throughout his career. It all began with his pre-Streetcar Named Desire performance in 1950's The Men (shown), for which Brando reportedly confined himself to a hospital bed for a month to get into his paraplegic character's psyche. Worth it? Yes (artistically at least). He was a real coot, but he's also one of the most respected actors in film history. —Lanford Beard

Natalie Portman

Role: Nina Sayers, Black SwanTechnique: To play the intense ballerina in Darren Aronofsky's 2010 thriller, Portman started preparing a year before the shoot, working out for six days a week for eight hours at a time. She also cut down on eating, and told EW, ''The whole thing, I'm aware that it's sick.''Worth it? Yes. She won the Oscar. (She also ended up marrying Benjamin Millepied, who performed in the movie and choreographed for it.) Still, her ballet cred was called into question when dancer Sarah Lane claimed that Portman only did 5 percent of the full body dancing shots. —Esther Zuckerman

Matt Damon

Role: Ilario, Courage Under FireTechnique: To play the heroin-addicted Gulf War veteran, Damon stuck to a brutal diet and training regimen. The actor's weight plummeted a shocking 40 pounds, threatening his life, putting him under medical supervision for months after filming ended, and messing up his metabolism for years. Worth it? Yes. Although Courage was snubbed by the awards, the film received positive reviews, and Damon impressed critics—among them, Francis Ford Coppola, who offered him the lead in The Rainmaker after seeing him as Ilario. A then-unknown Damon was on his way up in Hollywood. And neither he nor his weight have come down since. —Carolyn Todd

Daniel Day-Lewis

Roles: All of themTechnique: It was the start of something magnificent. To embody My Left Foot's protagonist Christy Brown, who has cerebral palsy and therefore can only use his left foot, Day-Lewis trained at a cerebral palsy clinic for weeks and then, once on set, never broke character by remaining in a wheelchair at all times. For 1992's The Last of the Mohicans, he killed all his own food; for 2012's Lincoln, he texted as the United States' 16th president and spoke only in Honest Abe's high-pitched timbre—both on and off set. Worth it? Without a doubt. He won his first Best Actor Oscar for My Left Foot and went on to become the winningest leading actor in film (two more trophies came for There Will Be Blood and Lincoln) thanks to his unflinching, mesmerizing devotion to his roles. —Ariana Bacle

Heath Ledger

Role: The Joker, The Dark KnightTechnique: Ledger holed himself up in hotel rooms for weeks at a time in preparation, where he tried out different voices and scribbled in a notebook as the Joker. Worth it? Yes and no. Heath Ledger's performance, one of his best and one of the best performances of the recent past, earned him universal critical acclaim and a posthumous Oscar. Still, many speculated in the wake of his death that his dedication to the part might have contributed to his sudden, tragic death from a drug overdose, thus robbing Ledger and the world of his talent.

Rooney Mara

Role: Lisbeth Salander, The Girl with the Dragon TattooTechnique: After a contentious casting process, relative newcomer Mara won the coveted role and almost immediately went full Goth—most notably enduring at least 12 piercings (including her nipple) in one day to fully immerse herself in the role. Worth it? Yes. Mara went from being known for playing Mark Zuckerberg's ex-girlfriend in The Social Network to earning an Oscar nomination for her role as Salander. While the film slightly underperformed at the box office to Sony's projections, it recouped its $90 million budget with a cool $232 million at the box office. Mara also gained a possible franchise out of the gambit—despite the average numbers at the box office, a sequel, The Girl Who Played With Fire, is still being written, with Mara up to reprise the role should the film go forward. —Teresa Jue

Dustin Hoffman

Role: Babe, Marathon ManTechnique: A legendary-yet-apocryphal yarn followed Hoffman for decades that his three-day jag to portray sleep-deprived Babe prompted costar Laurence Olivier to ask, '' Why don't you just try acting?'' In fact Hoffman later claimed he'd been the one to first utter those six wry words, getting a chuckle from Olivier. (Hoffman also attributed the bender to '' the days of wine and roses in Studio 54,'' not just acting.) Worth it? Yes. Hoffman was nominated for a Golden Globe for the part (Olivier, meanwhile, scored an Oscar nod for his simple ''acting'' technique) and has been in several in-the-skin performances since, including Oscar-winning turns in 1980's Kramer vs. Kramer and 1988's Rain Man. —Lanford Beard

Christian Bale

Roles: Several (it's kind of his jam)Technique: Though Bale's gone deep for many roles (The Fighter, American Hustle, Velvet Goldmine), the most striking was his 60-pound weight loss before portraying haunted insomniac Trevor Reznik in The Machinist (shown). By the time Bale reached his ''goal weight''— which he did by consuming just an apple a day and coffee—he looked scarily gaunt and was almost unrecognizable.Worth it? Mixed, leaning toward yes. Bale's performance as the paranoid and delusional Trevor was effectively eerie and strangely powerful and, although neither Bale nor The Machinist were nominated for any big awards, his commitment has netted him plenty of noms—and a Best Supporting Actor statuette for The Fighter. —Ariana Bacle

Robert De Niro

Role: Travis Bickle, Taxi DriverTechnique: Before his pendulum-like (and Oscar-winning) weight fluctuations for Raging Bull, De Niro lost 35 pounds and worked 12 hours a day as an NYC cab driver for a month before filming. To get inside the dark, tortured mind of Arthur Bremer, who partially inspired Bickle, De Niro recorded himself reading the would-be-assassin's diary and listened to it repeatedly. Worth it? Yes. De Niro's turn as a loner on-the-brink became iconic in American cinema. He scored Best Actor nominations from the Academy Awards and the Golden Globes. The film won the 1976 Cannes Palme d'Or and is one of Time magazine's top 100 movies of all time. —Carolyn Todd

Ashton Kutcher

Role: Steve Jobs, JobsTechnique: Kutcher adopted the late Jobs' infamous ''fruitarian diet,'' which is exactly what it sounds like. And while an apple a day may keep the doctor away, the actor discovered that the Apple founder's regiment of all apples all day will land you in the hospital—he was rushed to the ER for serious pancreatic issues and severe pain. Worth it? No. The box office bomb made $6.7 million in its opening weekend and was panned by critics. That said, many negative reviews noted that Kutcher's portrayal was admirable. —Carolyn Todd

Idris Elba

Role: Nelson Mandela, Mandela: Long Walk to FreedomTechnique: Elba slept alone for a night in a cell on Robben Island, South Africa, where the political prisoner spent 18 years. The actor had nothing but a thin blanket and a bowl (but no food or water). Doesn't sound that bad? Elba also became convinced the prison was haunted, tellingThe Daily Mail, ''I woke in the night, and a massive cold thing hit my face.'' Worth it? Yes. Though the biopic got mixed reviews, Elba's powerful performance nabbed him critical praise and a Best Actor nod at the Golden Globes. And, though ticket sales were tepid in the U.S., Mandela set a box office record in the peace activist's home country. —Carolyn Todd

Jared Leto

Role: Rayon, Dallas Buyers ClubTechnique: Along with the bones-baring star Matthew McConaughey, Leto starved his way to a gaunt 114 pounds for Dallas to play the transgendered, AIDS-afflicted Rayon. Equally admirable (and less harrowing) was Leto's round-the-clock embodiment of the fairer sex—he waxed his body and brows, and went grocery shopping as a woman. And that's not all: Leto shrank to a heroin addict's weight in Requiem for a Dream, then suffered gout after he ballooned by 67 pounds to play John Lennon's assassin in Chapter 27. Worth it? Yes. Leto won the Academy Award for Best Supporting Actor. Despite some pushback from the trans community, which wanted a transgender actor to play Rayon, Leto received rave reviews for his poignant performance. —Carolyn Todd

Halle Berry

Role: Vivian, Jungle FeverTechnique: One of the world's most beautiful women? Yeah, she visited a real crack den and didn't bathe for 10 days straight while shooting Spike Lee's 1991 romance (in which she played Vivian, a crack addict who turns to prostitution to support her habit). ''It's true,'' the Oscar winner told Wendy Williams in 2012. ''Ask Sam Jackson! He had to get a whiff of it.'' Worth it? Yes. Jungle Fever marked Berry's film debut, and her committed performance (in a generally well-reviewed movie) helped pave the way for bigger and better things. At least after she got B*A*P*S out of her system. —Hillary Busis

Min-sik Choi

Role: Dae-su Oh, OldboyTechnique: The prolific South Korean actor is said to have burned his own flesh for authenticity, and writer-director Chan-wook Park explained Buddhist Choi reconciled his beliefs with eating live octopus during filming by saying a prayer for each animal as it was killed. Worth it? Maybe. Choi's celebrity status in the States has remained mostly at cult level, though he did resurface in 2014's Lucy, another surefire cult favorite. —Lanford Beard

Al Pacino

Role: Frank Serpico, SerpicoTechnique: Be careful around Al Pacino when he's playing an undercover cop: About halfway through shooting the film, the future Oscar winner attempted to arrest a truck driver. (His crime? Driving his truck, and shooting exhaust into the street.) ''It was a fantasy for a moment,'' Pacino later remembered. ''I was going to put him under citizen's arrest, but then I realized what I was doing.''Worth it? Yup. Pacino won his first Best Actor Golden Globe for the part, and was also nominated for his first Best Actor Academy Award—though he wouldn't actually win moviemaking's biggest prize for another 19 years. —Hillary Busis

Eddie Redmayne

Role: Stephen Hawking, The Theory of EverythingTechnique: Playing Hawking, who suffers from a motor neuron disease, required that Redmayne intensely study the famed physicist and his movements and then replicate those movements. Redmayne ended up spending hours in a wheelchair with his body contorted, something that caused physical pain and sometimes affected his breathing. Worth it? Yes. Redmayne's performance is so on-point that Hawking himself has said it felt like watching himself on screen during certain parts of the film. And the media has been abuzz with talk that Redmayne could score an oscar nomination for Best Actor. —Ariana Bacle

Shia LaBeouf

Role: Boyd ''Bible'' Swan, FuryTechnique: Surprising absolutely no one, LaBeouf slashed his own face for Fury because he wasn't satisfied with the make-up approximation of Bible's war wounds. He also went to the dentist to get one of his teeth removed for the role, proving that LaBeouf just really doesn't trust stage make-up. Worth it? No. Sure, the movie started strong at the box office, but that's definitely not because LaBeouf's face wounds are real—and definitely not worth a voluntary trip to the dentist. —Ariana Bacle

Adrien Brody

Role: Wladyslaw Szpilman, The PianistTechnique: 6'5'' Brody whittled his weight down to a scant 130 pounds to play classical musician?turned?Warsaw ghetto prisoner Szpilman. He also practiced the piano for four hours a day until he could play Chopin flawlessly and tried to replicate Szpilman's isolation by jettisoning his cell phone, his car, and even (reportedly) his girlfriend during filming. At least he was no stranger to the Method approach: While filming 2005's The Jacket, Brody would ask to be left alone on a gurney, restrained in his character's titular straitjacket for long periods of time so he could stay in character. Worth it? Sometimes. Brody's devotion to verisimilitude in The Pianist helped him snag an Academy Award for Best Actor (and gave him an opportunity to smooch Halle Berry in front of all of Hollywood)—which, at 29, made him the youngest person in history to achieve that honor. The Jacket?well, it didn't fare so well with critics. —Hillary Busis

Hilary Swank

Role: Brandon Teena, Boys Don't CryTechnique: To prepare for her role as a transgender man, Swank acted and dressed like a man for weeks, refusing to let anyone see her out of character. Part of this transformation involving losing weight to highlight her angular facial features so she'd appear more boyish. Worth it? Yes. She won the Oscar for Best Actress that year. —Ariana Bacle